Relaxation protein glass transition

The proximity of this liquid-liquid transition to the protein-glass transition temperature is suggestive. Clearly, at temperatures below 220 K or so, the dynamics of water and protein are highly coupled. A recent computer simulation study has shown that the stmctural relaxation of protein requires relaxation of the water HB network and translational displacement of interfacial water molecules. It is, therefore, clear that the dynamics of water at the interface can play an important role. This is an interesting problem that deserves further investigation. 

The 1-2 cm 1 blue shift in the near-ambient spectra can be readily explained. Both B and B2 were found to blue shift nonexponentially with time after photolysis, with B experiencing a larger shift. This time-dependent blue shift is a consequence of the conformational relaxation that can occur under ambient conditions (39,46-48) but is inhibited at temperatures below the 185 K glass transition of the protein (24). Due to the similarity between the cryogenic and near-ambient temperature B-state center frequencies, the cryogenic B states appear to be the same as those measured near ambient temperature, but trapped within a conformationally unrelaxed protein. 

Much work has also been carried out on non-cereal plant proteins. Solid-state H and 2H NMR transverse relaxation measurements were used to investigate the effect of hydration on the plasticization of vicilin, legumin, and albumin fractions from peas.81 Their behaviour indicated that the plasticization of the globular legume proteins is considerably less than that found before for the linear barley protein C-hordein. The effects of microbial transglutaminase treatment on soy protein samples have been studied by H and solid-state 13C NMR spectroscopy, and its relation to the glass transition temperature was examined.82-83... 

At the molecular level, setting is a process of stress relaxation which results from the rearrangement of the protein macromolecules that form the flber. Under ambient conditions of water content and temperature, the matrix regions of wool are glass-like (ie below the glass-transition temperature, see Fig. 5). When fibers are deformed under these conditions, stress relaxation is slow. 

There are substantial difficulties in the interpretation of temperature-dependent shifts of protein spectra because of the thermal lability of proteins and the possibility of temperature-dependent conformational transitions. Low-temperature studies in aqueous solutions revealed that for many of the proteins investigated the observed shifts of the fluorescence spectra within narrow temperature ranges were probably the result of cooperative conformational transitions, and not of relaxational shifts/100 1 Spectral shifts have also been observed for proteins in glass-forming solvents, 01) but here there arise difficulties associated with the possible effects of viscous solvents on the protein dynamics. 

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